Found in Popular Electronics from the 90s, this circuit is based on a PLL567 and employs high-end or ultrasonic speakers depending on the frequency of oscillations.
This power source is indicated for the supply of the previous circuit (CB19638E), but it is also...
In the figure we have a circuit that uses unusual components, being indicated for low frequency...
This 300 Hz to 3.4 kHz filter was found in the May 1989 Radio Electronics magazine. The circuit...